1. Field of the Invention
The present invention relates to an electronic control device for a remote control (remote operation device) and a teleoperation system using the electronic control device. More specifically, the present invention relates to an electronic control unit (ECU) for a remote control and a teleoperation system using the ECU for use in a transport vehicle such as a boat.
2. Description of the Related Art
As local area network (LAN) for use in a transport vehicle such as a boat, a controller area network (CAN) in compliance with ISO 11898 is known. In a boat, for example, an ECU for a remote control in the cockpit and an ECU for an engine in the outboard motor are connected by a CAN cable as a two-line communication cable so that the outboard motor can be electrically and remotely controlled from the cockpit. See e.g., Japanese Patent Applications JP-A-2003-127985, JP-A-2003-146292, JP-A-2003-304265, JP-A-2004-217180, JP-A-2005-254849. JP Patent Application 2005-294352 (unpublished prior application).
A CAN cable has a high signal line and a low signal line. When a “0” signal is transmitted, the ECU sets the high signal line at a high level (3.5 V, for example) and the low signal line at a low level (21.5 V, for example). When a “1” signal is transmitted, the ECU sets the high signal line at a low level and the low signal line at a high level. The ECU detects the potential difference between the high signal line and the low signal line to determine whether the received signal is “0” or “1”.
When two ECUs are connected to each other as described above, there can occur a case where a signal is reflected at an end of the CAN cable and its waveform is distorted to cause a sudden communication failure during cruising. To prevent it, termination resistances (which are referred to also as “terminators”) are connected to both ends of the CAN. More specifically, each termination resistance is connected between the high signal line and the low signal line of the CAN cable.
When the construction of such a CAN is left to the user of the boat, the user can forget to connect the termination resistances. However, when the manufacturer of the boat constructs the CAN, there is almost no possibility of it.
Some boats have another cockpit above the cockpit. The lower, primary cockpit is called main station, and the other, upper cockpit is called sub-station. When there are two cockpits, each cockpit has an ECU for a remote control so that the outboard motor can be remotely operated from both the cockpits. In this case, the CAN cables are connected not in a star configuration but in a bus configuration. More specifically, the ECU for a remote control in the main station and the ECU for an engine are connected by a CAN cable, and the ECU for a remote control in the main station and the ECU for a remote control in the sub-station are connected by another CAN cable. In this case, termination resistances are connected, one each, to the ECU for an engine and the ECU for a remote control in the sub-station, but there is no need to connect a termination resistance to the ECU for a remote control in the main station.
In a two-station system having two ECUs for a remote control, when the sub-station has a failure, the user switches by himself or herself to a one-station system which uses only the ECU for a remote control in the main station so that the boat control in the main station cannot be adversely affected. In this case, however, it is often forgotten to connect a termination resistance to the ECU for a remote control in the main station. When no termination resistance is connected, the ECU for a remote control in the main station can operate but may malfunction as described before.